Hand held rotary tools are widely used by many people, including craftspeople, homeowners, and artists. These rotary tools typically include an outer housing designed to be easily held within a human hand. The housing retains an electric motor which is operable to drive a rotatable chuck of the rotary tool. The chuck allows a variety of accessories to be interchangeably used with the rotary tool.
To couple an accessory with the rotary tool, the chuck is rotated by a user to tighten the chuck about the shank of the accessory. The ability of the chuck to retain the shank of the accessory is dependent upon the amount of tightening torque applied by the user. When insufficient tightening torque is applied, the chuck will loosen under load resulting in a loss of control over the accessory which may damage either or both of the work piece and the accessory. To solve this issue, some chucks are provided with components that are tightened using keys or wrenches. While these alternatives allow for a much tighter grip on the shank of the accessory, the use of the alternatives increases the amount of time needed to switch accessories. Moreover, additional components, particularly smaller components such as keys and wrenches, are easily misplaced, leading to lost time in finding the items or in replacing the item.
In response to the problems with the known chuck systems, “quick change” collets were developed. The quick change collets capture a portion of the shank of an accessory within the collet, generally using a spring loaded sleeve which traps a ball bearing within a groove in the shank. The accessory is then driven by a portion of the bit holder within the collet that is shaped complimentary to the accessory shank. A common shape for a shank is that of a hexagon. Quick change collets significantly lower the time required to switch accessories and significantly reduce the potential of the accessory working loose from the rotary tool.
While quick change collets provide a number of benefits, known collet systems suffer from various limitations. One such limitation results from the manner in which the accessory shank is trapped. Specifically, in order to allow for insertion of the shaped shank within the shaped bit holder, the bit holder is necessarily larger than the shank. This results in some amount of play between the shank and the bit holder. As the amount of play increases, the potential for slippage and off-axis movement increases. As the amount of play decreases, the potential that foreign matter will interfere with the proper seating of the shank within the bit holder increases. Thus, a tradeoff is required between ease of use and performance.
Moreover, some amount of play is also required between the ball bearing and the groove in the shank. Thus, some amount of axial looseness between the accessory and the rotary tool is created. This looseness results in undesired axial shifts of the accessory when a load is placed on the rotary tool.
The foregoing limitations are further exacerbated by the engineering tolerances endemic to the production of rotary tool systems. As the tolerances are reduced, the cost of production increases. Accordingly, a tradeoff is required between achieving a cost effective tolerance while optimizing the performance of the system.
Accordingly, it would be advantageous to provide a collet and associated rotary tool system that is quick and easy to use and does not require the use of an additional tool such as a key or a wrench. It would be further advantageous if the collet and associated rotary tool system reduced the looseness of the accessory when the rotary tool is in use. It would also be advantageous if the collet and associated rotary tool system compensated for manufacturing tolerances while not being overly susceptible to inoperability due to the presence of foreign objects.